Okay, I think you have the right amount of credits now. On first try I got to the first boss with some credits to spare. Definitely not too hard for high-score/arcade gamers like myself.
I'll pop this on my flash cart and my wife and I will try to beat it tonight. We have been trying to master Flicky, so I think this will be a good fit.
The numbers up top are fine now because they don't flicker or flash. This game would have been an arcade hit in the mid eighties for sure.
This project really has a great feel to it.